Pdcch monitoring method and apparatus in a carrier junction system

ABSTRACT

A method is described for receiving a downlink control information (DCI) from a base station (BS) by a user equipment (UE) in a wireless communication system. The method includes monitoring a plurality of physical downlink control channel (PDCCH) candidates having the same payload size in a common search space and a UE-specific search space on a primary cell to receive the DCI. The common search space and the UE-specific search space are overlapped. If the UE is configured with a carrier indicator field (CIF), the method further includes determining that only a PDCCH in the common search space is transmitted from among the plurality of PDCCH candidates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of co-pending U.S. application Ser.No. 13/640,278 filed on Nov. 13, 2012, which is the National Phase ofPCT/KR2011/002462 filed on Apr. 7, 2011, which claims priority under 35USC 119(e) to U.S. Provisional Application No. 61/321,845 filed on Apr.7, 2010 and under 35 USC 119(a) to Korean Patent Application No.10-2011-0032138 filed in Republic of Korea, on Apr. 7, 2011. Thecontents of all of these applications are hereby incorporated byreference as fully set forth herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a carrier junction system, and moreparticularly, to a method and apparatus for monitoring a physicaldownlink control channel (PDCCH) in a carrier junction system.

2. Discussion of the Related Art

In the following description, 3GPP LTE (3rd generation partnershipprojecting long term evolution, hereinafter abbreviated LTE) and 3GPPLTE-Advanced (hereinafter abbreviated LTE-A) communication systems areschematically explained as an example of a mobile communication systemto which the present invention is applicable.

At least one cell exists in one eNode B. The cell is set to one ofbandwidths including 1.25 MHz, 2.5 MHz, 5 MHz. 10 MHz, 15 MHz, 20 MHzand the like and then provides an uplink or downlink transmissionservice to a plurality of user equipments. Different cells can be set toprovide different bandwidths, respectively. The eNode B controls datatransmission and reception for a plurality of user equipments. The eNodeB sends downlink scheduling information on downlink (DL) data to informa corresponding user equipment of time/frequency region for transmittingdata to the corresponding user equipment, coding, data size, HARQ(hybrid automatic repeat and request) relevant information and the like.In addition, the eNode B sends uplink scheduling information on uplink(UL) data to a corresponding user equipment to inform the correspondinguser equipment of a time/frequency region available for thecorresponding user equipment, coding, data size, relevant HARQinformation and the like. An interface for user or control traffictransmission is usable between eNode Bs.

Wireless communication technology has been developed up to LTE based onWCDMA (wideband code division multiple access) but the demands andexpectations of users and service providers are continuously rising.Since other radio access technologies are continuously developed, newtechnological evolution is required to remain competitive in the future.For this, reduction of cost per bit, service availability increase,flexible frequency band use, simple-structure and open interface,reasonable power consumption of user equipment and the like arerequired.

Recently, 3GPP is working on standardization of the next technology forLTE. In the present specification of the present invention, the nexttechnology shall be named ‘LTE-Advanced’ or ‘LTE-A’. Major differencesbetween the LTE system and the LTE-A system lie in system bandwidthdifference and relay introduction.

The LTE-A system has a goal of supporting a maximum broadband of 100MHz. For this, the LTE-A system uses carrier aggregation or bandwidthaggregation to achieve a broadband using a plurality of frequencyblocks. Carrier aggregation enables a plurality of frequency blocks tobe used as one large logical frequency band to use a wider frequencyband. A bandwidth of each frequency block can be defined based on asystem block used by the LTE system. In addition, each frequency blockis transmitted using a component carrier.

As a carrier aggregation technology is adopted in LTE-A, which is anext-generation communication technology, there is a need for a methodfor receiving, by a user equipment, a signal from an eNode B or a relayin a system which supports a plurality of carriers.

SUMMARY OF THE INVENTION

An object of the present invention devised to solve the problem lies ina method for resolving ambiguity in detection of downlink controlinformation (DCI) in a user equipment by detection of a plurality ofPDCCHs having the same size, in a section in which PDCCH search spacesoverlap (completely or partly), in a carrier junction system.

The object of the present invention can be achieved by providing amethod for monitoring a physical downlink control channel (PDCCH) in acarrier junction system, the method including monitoring a plurality ofcandidate PDCCHs in a section where a PDCCH search space of a firstcomponent carrier overlaps with a PDCCH search space of a secondcomponent carrier, and receiving downlink control information through aPDCCH having succeeded in blind decoding among the plurality ofcandidate PDCCHs, wherein the PDCCH having succeeded in the blinddecoding is a common PDCCH including common control information, a PDCCHfor a self-scheduling component carrier without a carrier indicatorfield (CIF), or a PDCCH for a primary component carrier.

Here, the monitoring performs blind decoding for the plurality ofcandidate PDCCHs, and the blind decoding performs CRC de-masking foreach of the candidate PDCCHs using a radio network temporary identifier(RNTI).

Further, the monitoring monitors the plurality of candidate PDCCHs basedon a PDCCH whose order of priority has been set in the overlappingsection.

The method further includes receiving information on the PDCCH whoseorder of priority has been set from a base station.

Further, the PDCCH, whose order of priority has been set, is the PDCCHhaving succeeded in the decoding.

The PDCCH having succeeded in the decoding is a common PDCCH in case thePDCCH search space of the first component carrier is a common searchspace monitored by all user equipments (UEs) within a cell, and thePDCCH search space of the second component carrier is a UE-specificsearch space monitored by at least one of the UEs within the cell.

The PDCCH having succeeded in the decoding is a PDCCH without a carrierindicator field (CIF) in case both the PDCCH search space of the firstcomponent carrier and the PDCCH search space of the second componentcarrier are a UE-specific search space.

The common PDCCH is transmitted in the common search space of the firstcomponent carrier.

The first component carrier is a primary component carrier.

The primary component carrier is an uplink component carrier linked witha PDCCH monitoring component carrier where the PDCCH is transmitted, acomponent carrier having a first linkage with the PDCCH monitoringcomponent carrier, or a downlink or uplink component carrier whichbecomes an object of self-scheduling in the PDCCH monitoring carrier.

In case there are a plurality of the PDCCH monitoring componentcarriers, the primary component carrier is defined for each of theplurality of PDCCH monitoring component carriers.

In another aspect of the present invention, there is provided a userequipment (UE) in a carrier aggregation system, the UE including a radiofrequency (RF) unit for transmitting and receiving a radio signal, and acontroller linked with the RF unit, wherein the controller monitors aplurality of candidate physical downlink control channels (PDCCHs) in asection where a PDCCH search space of a first component carrier overlapswith a PDCCH search space of a second component carrier, and controlsthe RF unit to receive downlink control information through a PDCCHhaving succeeded in blind decoding among the plurality of PDCCHs,wherein the PDCCH having succeeded in the blind decoding is a commonPDCCH including common control information, a PDCCH for aself-scheduling component carrier without a carrier indicator field(CIF), or a PDCCH for a primary component carrier.

Here, the controller monitors the plurality of candidate PDCCHs usingblind decoding, and the blind decoding performs CRC de-masking for eachof the candidate PDCCHs using a radio network temporary identifier(RNTI).

The controller monitors the plurality of candidate PDCCHs based on aPDCCH whose order of priority has been set in the overlapping section.

The controller controls the RF unit to receive information on the PDCCHwhose order of priority has been set from a base station.

The PDCCH, whose order of priority has been set, is the PDCCH havingsucceeded in the decoding.

The PDCCH having succeeded in the decoding is a common PDCCH in case thePDCCH search space of the first component carrier is a common searchspace monitored by all user equipments within a cell, and the PDCCHsearch space of the second component carrier is a UE-specific searchspace monitored by at least one of the user equipments within the cell.

The PDCCH having succeeded in the decoding is a PDCCH without a carrierindicator field (CIF) in case both the PDCCH search space of the firstcomponent carrier and the PDCCH search space of the second componentcarrier are a UE-specific search space.

The first component carrier is a primary component carrier.

According to the present invention, in a section where PDCCH searchspaces overlap or are shared, the ambiguity of detection of DCIs havingthe same size in the overlapping or shared section can be resolved byperforming blind decoding for a plurality of candidate PDCCHs based onpredetermined PDCCHs using priority, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates physical channels used in a 3GPP system and a generalsignal transmission method using the channels.

FIG. 2 illustrates a configuration of a radio frame used in a 3GPP LTEsystem which is an example of a mobile communication system.

FIGS. 3( a) and 3(b) illustrate the configuration of a downlink anduplink subframe of a 3GPP LTE system which is an example of a mobilecommunication system.

FIG. 4 illustrates a time-frequency resource grid structure of adownlink used in the present invention.

FIG. 5 is a block diagram illustrating the configuration of a PDCCH.

FIG. 6 illustrates an example of resource mapping of a PDCCH.

FIG. 7 illustrates CCE interleaving in a system band.

FIG. 8 illustrates a monitoring of a PDCCH.

FIG. 9( a) illustrates a concept that a plurality of MACs manage amulti-carrier, and FIG. 9( b) illustrates a concept that a plurality ofMACs manage a multi-carrier.

FIG. 10( a) illustrates a concept that one MAC manages a multi-carrierin a base station, and FIG. 10( b) illustrates a concept that one MACmanages a multi-carrier in a user equipment.

FIG. 11 illustrates an example of a multiple carrier.

FIG. 12 illustrates an example of cross-carrier scheduling.

FIG. 13 illustrates an example of a component carrier (CC) set.

FIGS. 14( a) and 14(b) illustrate a method for linking a DL CC includedin a PDCCH monitoring CC set with a CC which transmits a PDSCH/PUSCH.

FIGS. 15( a) and 15(b) illustrate a method 3 (modified method 1) whichwill be described later.

FIG. 16( a) illustrates an example in which ambiguity of DCI occurs incase a common search space (CSS) for CC #1 and a UE-specific searchspace (USS) for CC #2 overlap.

FIG. 16( b) illustrates an example where ambiguity of a DIC occurs incase a UE-specific search space for CC #1 and a UE-specific search spacefor CC#2 completely overlap.

FIG. 16( c) illustrates an example in which ambiguity of a DCI occurs incase a UE-specific search space for CC #1 and a UE-specific search spacefor CC #2 partially overlap.

FIG. 16( d) illustrates an example in which ambiguity of a DCI occurs incase a UE-specific search space for CC #1 and a UE-specific search spacefor CC #2 are shared.

FIG. 17 illustrates a shifting of an overlapping section to preventoverlap between a CSS and a USS when the CSS is overlapped with the USSaccording to an embodiment of the present invention.

FIG. 18 illustrates a configuration of a search space to prevent overlapof the search spaces by CCs according to another embodiment of thepresent invention.

FIG. 19( a) illustrates a method for detecting a DCI corresponding to aCSS in an overlapping section in case the CSS overlaps with a USS

FIG. 19( b) illustrates a method for detecting a DCI for aself-scheduling CC in an overlapping section in case search spacesbetween USSs completely overlap with each other.

FIG. 19( c) illustrates a method for detecting a DCI for aself-scheduling CC in an overlapping section in case the search spacesbetween USSs partially overlap.

FIG. 19( d) illustrates a method for detecting a DCI for aself-scheduling CC in a shared section in case USSs of different CCs areshared

FIG. 20 is a block diagram illustrating a radio communication systemaccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. It should be understood that the present invention is notlimited solely to the following embodiment. The following descriptionincludes specific details for providing a full understanding of thepresent invention. However, it will be apparent to anyone skilled in theart that the present invention may also be embodied without suchspecific details. For example, the following detailed description ismade under the assumption that the mobile telecommunications systemcorresponds to an IEEE 802.16 system. However, with the exception of thecharacteristic features of the IEEE 802.16 system, the present inventionmay also be applied to any other mobile telecommunications system.

In some cases, to avoid any ambiguity in the concept of the presentinvention, structures or devices of the disclosure may be omitted, orthe embodiment of the present invention may be illustrated in the formof block views focusing on the essential functions of each structure anddevice. Also, wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

Accordingly, in the following description of the present invention, itis assumed that a user equipment collectively refers to mobile or fixeduser-end equipment (or device), such as an AMS (Advanced MobileStation), UE (User Equipment), MS (Mobile Station), and so on. Also, itis assumed that a base station collectively refers to a random node,such as a Node B, eNode B, Base Station, AP (Access Point), and so on,of a network end communicating with a terminal.

Generally, in a mobile communication system, a user equipment and arelay are able to receive information in downlink from a base station.In addition, the user equipment and the relay are able to transmitinformation in uplink as well. The information transmitted or receivedby the user equipment and the relay includes data and various kinds ofcontrol information. In addition, various physical channels existaccording to a type usage of the information transmitted or received bythe user equipment and the relay.

FIG. 1 is a diagram explaining physical channels used for such a mobilecommunication system as 3GPP (3rd generation partnership project) systemand a general signal transmitting method using the physical channels.

A user equipment, which is initially activated or which enters a newcell, performs an initial cell search for matching synchronization witha base station or the like (S101). For this, the user equipment matchesthe synchronization with the base station by receiving a primarysynchronization channel (P-SCH) and a secondary synchronization channel(S-SCH) from the base station and then obtains such information as cellID and the like. Subsequently, the user equipment is able to obtainintra-cell broadcast information by receiving a physical broadcastchannel from the base station. Meanwhile, the user equipment is able tocheck a downlink channel status by receiving a downlink reference signal(DL RS) in the initial cell search step.

Having completed initial cell search, the user equipment is able toobtain further detailed system information by receiving a physicaldownlink control channel (PDCCH) and a physical downlink shared channel(PDSCH) according to the physical downlink control channel information(S102).

Meanwhile, the user equipment failing to complete access to the basestation is able to perform such a random access procedure as steps S103to S106 to complete access to the base station. For this, the userequipment transmits a feature sequence as a preamble via a physicalrandom access channel (PRACH) (S103 and S105) and is then able toreceive a response message in response to the random access via aphysical downlink control channel and a physical downlink shared channelcorresponding to the physical downlink control channel (S104 and S106).Subsequently, in case of contention based random access (except duringhandover), it is able to additionally perform such a contentionresolution procedure.

Having performed the above procedures, the user equipment is able toperform general uplink/downlink signal transmission procedures includinga physical downlink control channel/physical downlink shared channelreception (S107) and a physical uplink shared channel/physical uplinkcontrol channel (PUSCH/PUCCH) transmission (S108). The informationtransmitted by the UE to the base station through uplink or theinformation received by the UE from the base station includes adownlink/uplink ACK/NACK signal, a channel quality indicator (CQI), aprecoding matrix index (PMI), a rank indicator (RI), etc. In the case ofa 3GPP LTE system, the UE may transmit information such as the abovementioned CQI, RMI and RI information, etc. through the PUSCH and/orPUCCH.

FIG. 2 shows the structure of a radio frame used in the 3GPP LTE systemas an exemplary mobile communication system.

Referring to FIG. 2, one radio frame has a length of 10 ms (327200 Ts)and includes ten subframes having an equal size. Each subframe has alength of 1 ms and includes two slots each having a length of 0.5 ms(15360 Ts). Here, Ts denotes a sampling time, which is represented asTx=1/(15 kHz×2048)=3.2552×10−8 (approximately 33 ns). A slot includes aplurality of Orthogonal Frequency Division Multiplexing (OFDM) symbolsor Single Carrier-Frequency Division Multiple Access (SC-FDMA) symbolsin the time domain and a plurality of resource blocks in the frequencydomain.

In the LTE system, one resource block includes 12 subcarriers×7(6) OFDMsymbols or SC-FDMA symbols. A unit time for transmitting data, TransmitTime Interval (TTI), may be set to one or more subframes. Theabove-described radio frame structure is exemplary and the number ofsubframes included in the radio frame, the number of slots included inone subframe, and the number of OFDM symbols or SC-FDMA symbols includedin each slot may be changed in various manners.

FIG. 3 shows the structures of uplink and downlink subframes in the 3GPPLTE system as an exemplary mobile communication system.

Referring to FIG. 3( a), one downlink subframe includes two slots in thetime domain. A maximum of three OFDM symbols located in a front portionof a first slot in the downlink subframe correspond to a control regionallocated with control channels, and the remaining OFDM symbolscorrespond to a data region allocated with a Physical Downlink SharedChannel (PDSCH).

Examples of downlink control channels used in the 3GPP LTE include aPhysical Control Format Indicator Channel (PCFICH), a Physical DownlinkControl Channel (PDCCH), a Physical Hybrid-ARQ Indicator Channel(PHICH), etc. The PCFICH is transmitted at a first OFDM symbol of asubframe and carries information regarding the number of OFDM symbols(i.e., a control region size) used for transmission of control channelswithin the subframe. Control information transmitted over the PDCCH isreferred to as downlink control information (DCI). The DCI includesuplink resource allocation information, downlink resource allocationinformation, and an uplink transmit power control command for arbitraryuser equipment (UE) groups. The PHICH carries anacknowledgement/negative-acknowledgement (ACK/NACK) signal with respectto uplink Hybrid Automatic Repeat Request (HARQ). That is, an ACK/NACKsignal with respect to uplink data sent from a UE is transmitted overthe PHICH.

A description will be given of a PDCCH corresponding to a downlinkphysical channel below. The PDCCH will be described in more detail laterwith reference to FIGS. 5 to 8.

The PDCCH can carry a resource allocation and transmission format of aPDSCH (which may be referred to as a DL grant), resource allocationinformation of a PUSCH (which may be referred to as a UL grant), a setof transmit power control commands on individual UEs within an arbitraryUE group, activation of a Voice over Internet Protocol (VoIP). etc. Aplurality of PDCCHs can be transmitted within a control region. A UE canmonitor the PDCCHs. The PDCCH includes an aggregate of one or severalconsecutive Control Channel Elements (CCEs).

The PDCCH can be transmitted in the control region after subblockinterleaving. A CCE is a logical allocation unit used to provide thePDCCH with a coding rate based on a state of a radio channel. The CCEcorresponds to a plurality of resource element groups. A format of thePDCCH and the number of bits of the available PDCCH are determinedaccording to a correlation between the number of CCEs and the codingrate provided by the CCEs.

Control information carried on the PDCCH is called DCI. Table 1 showsDCI according to DCI format.

TABLE 1 DCI Format Description DCI Format 0 used for the scheduling ofPUSCH DCI Format 1 used for the scheduling of one PDSCH codeword DCIFormat 1A used for the compact scheduling of one PDSCH codeword andrandom access procedure initiated by a PDCCH order DCI Format 1B usedfor the compact scheduling of one PDSCH codeword with precodinginformation DCI Format 1C used for very compact scheduling of one PDSCHcodeword DCI Format 1D used for the compact scheduling of one PDSCHcodeword with precoding and power offset information DCI Format 2 usedfor scheduling PDSCH to UEs configured in closed-loop spatialmultiplexing mode DCI Format 2A used for scheduling PDSCH to UEsconfigured in open-loop spatial multiplexing mode DCI Format 3 used forthe treansmission of TPC commands for PUCCH and PUSCH with 2-bit poweradjustments DCI Format 3A used for the treansmission of TPC commands forPUCCH and PUSCH with single bit power adjustments

DCI format 0 conveys uplink resource allocation information, DCI format1 to DCI format 2 are used to indicate downlink resource allocationinformation, and DCI format 3 and DCI format 3A indicate uplink transmitpower control (TPC) command for UE groups.

A method for mapping resources for transmission of a PDCCH by a basestation in an LTE system will be briefly described below.

Generally, a base station may transmit scheduling allocation informationand other control information through a PDCCH. The physical controlchannel may be transmitted to one aggregation or a plurality ofcontinuous control channel elements (CCE). One CCE includes nineresource element groups (REG). The number of RBGs, which are notallocated to a physical control format indicator channel (PCFICH) or aphysical hybrid automatic repeat request indicator channel (PHICH), isNREG. The CCE, which is available in the system, is from 0 to NCCE-1(here, N_(CCE)=└N_(REG)/9┘). The PDCCH supports a multiple format asshown in Table 3 below. One PDCCH, which comprises n consecutive CCEs,starts from CCE, which performs i mod n=0 (here, i is CCE number).Multiple PDCCHs may be transmitted to one subframe.

TABLE 2 PDCCH Number of Number of resource- Number of format CCEselement groups PDCCH bits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

Referring to Table 2, a base station may determine the PDCCH formataccording to the number of areas to which control information, etc. willbe sent. The UE may reduce overhead by reading control information, etc.in CCE units. Likewise, even the relay may read control information,etc. in R-CCE units. In the LTE-A system, in order to transmit anR-PDCCH for an arbitrary relay, resource elements may be mapped in R-CCE(Relay-Control Channel Element) units.

Referring to FIG. 3( b). an uplink subframe can be divided in thefrequency domain into a control region and a data region. The controlregion is allocated with a PUCCH for carrying uplink controlinformation. The data region is allocated with a PUSCH for carrying userdata. To maintain a single carrier property, one UE does notsimultaneously transmit the PUCCH and the PUSCH. The PUCCH for one UE isallocated to an RB pair in a subframe. RBs belonging to the RB pairoccupy different subcarriers in two respective slots. The RB pairallocated to the PUCCH is frequency-hopped at a slot boundary.

FIG. 4 shows a downlink time-frequency resource grid structure used inthe present invention.

A downlink signal transmitted in each slot may be described by aresource grid including N_(RB) ^(DL)×N_(SC) ^(RB) subcarriers andS_(symb) ^(DL) OFDM symbols. N_(RB) ^(DL) indicates the number ofdownlink resource blocks (RBs), N_(SC) ^(DL) represents the number ofsubcarriers which configure one RB, and N_(symb) ^(DL) indicates thenumber of OFDM symbols in one downlink slot. N_(RB) ^(DL) depends on adownlink transmission bandwidth set in a corresponding cell and needs tosatisfy N_(RB) ^(min,DL)≦N_(RB) ^(DL)≦N_(RB) ^(max,DL). Here, N_(RB)^(min,DL) indicates a minimum downlink bandwidth supported by a wirelesscommunication system, and N_(RB) ^(max,DL) represents a maximum downlinkbandwidth supported by the wireless communication system. While N_(RB)^(min,DL) may be 6 and N_(RB) ^(max,DL) may be 110, they are not limitedthereto. The number of OFDM symbols included in one slot may depend onthe length of a Cyclic Prefix (CP) and a subcarrier interval. In case ofmulti-antenna transmission, one resource grid can be defined per antennaport.

An element in the resource grid for each antenna port is called aResource Element (RE) and uniquely identified by an index pair (k, l) ina slot. Here, k indicates a frequency-domain index ranging from 0 toN_(BR) ^(DL)N_(SC) ^(RB)−1, and l indicates a time-domain index rangingfrom 0 to N_(symb) ^(DL)−1.

An RB shown in FIG. 4 is used to describe the mapping relationshipbetween a physical channel and REs. RBs may be classified into aphysical RB (PRB) and a virtual RB (VRB). One PRB is defined as N_(symb)^(DL) consecutive OFDM symbols in the time domain and N_(SC) ^(RB)consecutive subcarriers in the frequency domain. Here, N_(symb) ^(DL)and N_(SC) ^(RB) may be predetermined values. For example, N_(symb)^(DL) and N_(SC) ^(RB) may have values as shown in the following Table3. Accordingly, one PRB includes N_(symb) ^(DL)×N_(sc) ^(RB) REs. Whileone PRB can correspond to one slot in the time domain and correspond to180 kHz in the frequency domain, it is not limited thereto.

TABLE 3 Configuration N_(sc) ^(RB) N_(symb) ^(DL) Normal Δf = 15 kHz 127 cyclic prefix Extended Δf = 15 kHz 6 cyclic prefix Δf = 7.5 kHz 24 3

One PRB has a value in the range of 0 to N_(RB) ^(DL)−1 in the frequencydomain. The relationship between a PRB number n_(PRB) in the frequencydomain and a resource element (k, l) in one slot satisfies

  ? = ⌊?⌋ ?indicates text missing or illegible when filed

The VRB has a size equal to the PRB. The VRB can be classified into alocalized VRB (LVRB) and a distributed VRB (DVRB). For each VRB type, apair of VRBs in two slots of one subframe are allocated a single VRBnumber n_(VRB).

The VRB may have a size equal to the PRB. For each of the LVRB and DVRB,a pair of VRB having a single VRB index (which may be referred to as aVRB number) are allocated to two slots in one subframe. In other words,N_(RB) ^(DL) VRBs which belong to the first one of two slots in onesubframe are allocated with one of indexes in the range of 0 to N_(RB)^(DL)−1, and N_(RB) ^(DL) VRBs which belong to the second slot are alsoallocated with one of the indexes in the range of 0 to N_(RB) ^(DL)−1.

The radio frame structure, the downlink subframe and uplink subframe,the time-frequency resource grid structure, etc. disclosed in FIGS. 2 to4 may also be applied between the base station and the relay.

Hereinafter, a process, in which the base station sends the PDCCH to theUE, will be described.

FIG. 5 illustrates a block diagram illustrating a configuration of aPDCCH.

The base station determines the PDCCH format according to the DCI to betransmitted to the UE, attaches the cyclic redundancy check (CRC) to theDCI, and masks a unique identifier (also referred to as a radio networktemporary identifier (RNTI)) to the CRC according to the owner or theuse of the PDCCH (510).

In case of a PDCCH for a specific UE, the UE's unique identifier, e.g.,a cell-RNTI (C-RNTI) may be masked to the CRC. Further, in the case ofthe PDCCH for a paging message, a paging indication identifier, e.g., apaging-RNTI (P-RNTI) may be masked to the CRC. In the case of a PDCCHfor system information, a system information-RNTI (SI-RNTI) may bemasked to the CRC. A random access-RNTI (RARNTI) may be masked to theCRC to indicate a random access response which is a response totransmission of a random access preamble of the UE. In order to indicatethe transmit power control (TPC) command for a plurality of UEs, aTPC-RNTI may be masked to the CRC.

If the C-RNTI is used, the PDCCH carries control information for acorresponding specific UE (referred to as UE-specific controlinformation), and if another RNTI is used, the PDCCH carries commoncontrol information received by all or a plurality of UEs within thecell.

The CRC generates coded data by encoding the DCI (520). The encodingincludes channel encoding and rate matching.

The coded data is modulated, thereby generating modulation symbols(530).

The modulation symbols are mapped to physical resource elements (RE)(540). Each of the modulation symbols is mapped to the RE.

FIG. 6 illustrates an example of the resource mapping of the PDCCH.

Referring to FIG. 6, R0 is a standard signal of a first antenna, R1 is astandard signal of a second antenna, R2 is a standard signal of a thirdantenna, and R3 is a standard signal of a fourth antenna.

The control region within the subframe includes a plurality of controlchannel elements (CCE). The CCE is a logical allocation unit used toprovide the PDCCH with the coding rate, and corresponds to a pluralityof resource element groups (REG). The REG includes a plurality ofresource elements. The PDCCH format and the possible number of bits ofthe PDCCH are determined according to the correlation between the numberof CCEs and the coding rate provided by the CCEs.

One REG (indicated as a quadruplet in the drawings) includes four REs,and one CCE includes 9 REGs. In order to constitute one PDCCH, {1, 2, 4,8}CCEs may be used, and each element of {1, 2, 4, 8} is called a CCEaggregation level.

The control channel, which comprises one or more CCEs, performsinterleaving in REG units, and is mapped to the physical resources aftera cyclic shift based on the cell identifier is performed.

FIG. 7 illustrates an example of dispersing CCEs in a system band.

Referring to FIG. 7, a plurality of logically consecutive CCEs is inputto an interleaver. The interleaver performs a function of mixing theplurality of input CCEs in REG units.

Hence, the frequency/time resources, which form one CCE, are physicallyscattered in the entire frequency/time domain within the control regionof the subframe. As such, the control channel is configured in CCEunits, but interleaving is performed in REG units, and thus frequencydiversity and interference randomization gain may be maximized.

FIG. 8 illustrates monitoring of a PDCCH.

In 3GPP LTE, blind decoding is used for detection of a PDCCH. The blinddecoding is a scheme of checking the CRC error and determining whetherthe PDCCH is its own control channel by de-masking a desired identifierto the CRC of the received PDCCH (referred to as a PDCCH candidate). TheUE does not recognize at which position within the control region itsown PDCCH is transmitted using which CCE set level or DCI format.

A plurality of PDCCHs may be transmitted within one subframe. A UEmonitors a plurality of PDCCHs for each subframe. Here, the monitoringattempts decoding of the PDCCH according to the monitored PDCCH format.

In 3GPP LTE, in order to reduce a burden due to blind decoding, a searchspace is used. The search space is a monitoring set of a CCE for thePDCCH. The UE monitors the PDCCH within a corresponding search space.

The search space is divided into a common search space and a UE-specificsearch space. The common search space, as a space for searching for aPDCCH having common control information, comprises 16 CCEs of indexes 0to 15, and supports a PDCCH having {4, 8} CCE set level. However, aPDCCH (DCI format 0, 1), which carries UE-specific information, may betransmitted in the common search space. The UE-specific search spacesupports a PDCCH having a CCE set level of {1, 2, 4, 8}.

Table 4 below shows the number of PDCCH candidates monitored by the UE.

TABLE 4 Number Search Space Aggregation Size of PDCCH DCI Type level L[in CCEs] candidates formats UE-specific 1 6 6 0, 1, 1A, 1B, 2 12 6 1D,2, 2A 4 8 2 8 16 2 Common 4 16 4 0, 1A, 1C, 8 16 2 3/3A

The size of the search space is determined by the above Table 4, and inthe start point of the search space, the common search space and theUE-specific search space are differently defined. The start point of thecommon search space is fixed regardless of the subframe, but the startpoint of the UE-specific search space may be changed per subframeaccording to the UE identifier (e.g., C-RNTI), the CCE set level and/orthe slot number within the radio frame. In case the start point of theUE-specific search space is located in the common search space, theUE-specific search space may be overlapped with the common search space.

In the set level Lε{1,2,3,4}, the search space S(L) k is defined as aset of PDCCH candidates. The CCE corresponding to the PDCCH candidate mof the search space S(L) k is given as follows.

L·{(Y _(k) +m)mod └N _(CCB,k) /L┘}+i  Formula 1

Here, i=0, 1, . . . , L−1, m=0, . . . , M^((L))−1, and N_(CCE,k) is thetotal number of CCEs which can be used in transmission of the PDCCHwithin the control region of subframe k. The control region includes aset of CCEs numbered 0 to N_(CCE,k)−1. M^((L)) is the number of PDCCHcandidates in the CCE set level L in the given search space. In thecommon search space, Yk is two set levels, and is set to 0 for L=4 andL=8. In the UE-specific search space of set level L, variable Yk may bedefined as follows.

Y _(k)=(A·Y _(k-1))mod I)  Formula 2

Here, Y−1=n_(RNTI)≠0, A=39827, D=65537, k=floor (n_(s)/2), and ns is aslot number within the radio frame.

When the UE monitors the PDCCH using the PDCCH, the DCI format andsearch space, which should be monitored according to the transmissionmode of the PDSCH, are determined.

Table 5 below shows an example of PDCCH monitoring where C-RNTI is set.

TABLE 5 Transmission Transmission mode of PDSCH mode DCI format Searchspace according to PDCCH Mode 1 DCI format 1A Common and Single antennaport, port 0 UE specific DCI format 1 UE specific Single antenna port,port 0 Mode 2 DCI format 1A Common and transmit diversity UE specificDCI format 1 UE specific transmit diversity Mode 3 DCI format 1A Commonand transmit diversity UE specific DCI format 2A UE specific cyclicdelay diversity (CDD or transmit diversity Mode 4 DCI format 1A Commonand transmit diversity UE specific DCI format 2 UE specific closed-loopspatial multiplexing Mode 5 DCI format 1A Common and transmit, diversityUE specific DCI format 1D UE specific closed-loop spatial multiplexingMode 6 DCI format 1A Common and transmit diversity UE specific DCIformat 1B UE specific closed-loop spatial multiplexing Mode 7 DCI format1A Common and if the number of PBCH transmit ports is UE specific 1,single antenna port, port 0, otherwise, transmit diversity DCI format 1UE specific single antenna port, port 5 Mode 8 DCI format 1A Common andif the number of PBCH transmit ports is UE specific 1, single antennaport, port 0, otherwise, transmit diversity DCI format 2B UE specificdual layer transmit (port 7 or 8), or single antenna port, port 7 orport 8

When the UE monitors the PDCCH using SPS C-RNTI, the search space andDCI format to be monitored are determined according to the transmissionmode of the PDSCH.

Table 6 below shows an example of PDCCH monitoring in which the SPSC-RNTI is set.

TABLE 6 PDCCH and PDSCH configured by SPS C-RNTI TransmissionTransmission scheme of PDSCH mode DCI format Search Space correspondingto PDCCH Mode 1 DCI format 1A Common and Single-antenna port, port 0(see UE specific by C-RNTI subclause 7.1.1) DCI format 1 UE specific byC-RNTI Single-antenna port, port 0 (see subclause 7.1.1) Mode 2 DCIformat 1A Common and Transmit diversity (see subclause 7.1.2) UEspecific by C-RNTI DCI format 1 UE specific by C-RNTI Transmit diversity(see subclause 7,1.2) Mode 3 DCI format 1A Common and Transmit diversity(see subclause 7.1.2) UE specific by C-RNTI DCI format 2A UE specific byC-RNTI Transmit diversity (see subclause 7.1.2) Mode 4 DCI format 1ACommon and Transmit diversity (see subclause 7.1.2) UE specific byC-RNTI DCI format 2 UE specific by C-RNTI Transmit diversity (seesubclause 7.1.2) Mode 5 DCI format 1A Common and Transmit diversity (seesubclause 7.1.2) UE specific by C-RNTI Mode 6 DCI format 1A Common andTransmit diversity (see subclause 7.1.2) UE specific by C-RNTI Mode 7DCI format 1A Common and Single-antenna port; port 5 UE specific byC-RNTI DCI format 1 UE specific by C-RNTI Single-antenna port; port 5

Table 7 below shows an example of PDCCH monitoring where the SPS C-RNTIis set.

TABLE 7 PDCCH configured by SPS C-RNTI DCI format Search Space DCIformat 0 Common and UE specific by C-RNTI

Hereinafter, a multiple carrier system will be described.

A 3GPP LTE system supports a case where the downlink band and the uplinkband are differently set, but this is based on one component carrier(CC).

This means that, in a situation in which one CC is defined for downlinkand uplink, 3GPP LTE is supported only when the bandwidth of thedownlink and the bandwidth of the uplink are the same or are differentfrom each other. For example, 3GPP LTE supports a maximum bandwidth of20 MHz, and the uplink bandwidth and the downlink bandwidth may bedifferent, but only one CC is supported for uplink and downlink.

The spectrum aggregation (or referred to as bandwidth aggregation orcarrier aggregation) is to support a plurality of CCs. Spectrumaggregation is introduced to support throughput, prevent cost increasedue to introduction of a broadband radio frequency (RF) device, andsecure compatibility with an existing system. For example, if 5 CCs areallocated as the granularity of the carrier unit having a bandwidth of20 MHz, the maximum bandwidth of 100 MHz may be supported.

Spectrum aggregation may be divided into contiguous spectrum aggregationmade between continuous carriers and non-contiguous spectrum aggregationmade between non-continuous carriers in a frequency domain. The numberof CCs aggregated between downlink and uplink may be differently set.When the number of the uplink CCs and the number of the downlink CCs arethe same, the aggregation is called symmetric aggregation, and when thenumbers are different, the aggregation is called asymmetric aggregation.

Further, the component carrier may be called “cell”.

Specifically, the “cell” may mean a pair of a downlink component carrierand an uplink component carrier. Here, the uplink component carrierrefers to a component carrier which has been linked with the downlinkcomponent carrier.

Further, the “cell” may also mean only a downlink component carrier.

That is, the “cell” may be used as a concept of a pair of a DL CC and aUL CC or as a term meaning only a DL CC. Here, the “cell” should bedistinguished from a “cell” as a generally used area covered by a basestation.

Hereinafter, the “cell” and the component carrier are used together andmay be understood as the same concept.

The sizes of the CCs (i.e., bandwidth) may be different. For example,when 5 CCs are used to constitute a 70 MHz band, a possibleconfiguration is 5 MHz carrier (CC #0)+20 MHz carrier (CC #1)+20 MHzcarrier (CC #2)+20 MHz carrier (CC #3)+5 MHz carrier (CC #4).

The configuration of a physical layer (PHY) and layer 2 (MAC) fortransmission on a plurality of uplink or downlink carrier bands, whichhave been allocated from the perspective of an arbitrary cell or UE, isshown in FIGS. 9 and 10.

FIG. 9( a) illustrates a concept of managing a multi-carrier by aplurality of MACs in a base station, and FIG. 9( b) illustrates aconcept of managing a multi-carrier by a plurality of MACs in a UE.

As shown in FIGS. 9( a) and 9(b), each MAC may control each carrier by1:1.

In a system which supports a plurality of carriers, each carrier may beused in a contiguous or non-contiguous manner. This may be appliedregardless of the distinction between uplink and downlink. The TDDsystem may be configured to operate N carriers including transmission ofthe downlink and the uplink in each carrier, and the FDD system isconstituted to use a multiple of carriers in uplink and downlink,respectively. In the case of the FDD system, the number of carriersaggregated in uplink and downlink and/or carrier aggregation ofasymmetric carriers with different bandwidths may be supported.

FIG. 10( a) illustrates a concept of managing a multi-carrier by one MACby a base station, and FIG. 10( b) illustrates a concept of managing amulti-carrier by one MAC in a UE.

Referring to FIGS. 10( a) and 10(b), one MAC performs transmission andreception by managing and operating one or more frequency carriers.Since frequency carriers managed in one MAC do not need to be contiguousto each other, resource management is more flexible which isadvantageous. In FIGS. 10( a) and 10(b). one PHY is set to mean onecomponent carrier for convenience of explanation. Here, one PHY does notnecessarily mean an independent radio frequency (RF) device. Generally,one independent RF device means one PHY, but is not necessarily limitedthereto, and one RF may include several PHYs.

Further, a series of downlink control channels (PDCCH), which transmitcontrol information of L1/L2 control signaling generated from the packetscheduler of the MAC layer to support the configuration in FIGS. 10( a)and 10(b), may be mapped to the physical resource within the individualcomponent carrier, and then transmitted.

At this time, particularly, the PDCCH about the control information,which is related with the grant or channel allocation related with thePUSCH or the individual unique PDSCH, may be generated as an encoded anddistinguished PDCCH by being distinguished by component carriers inwhich the physical shared channel is transmitted. This is called aseparate coded PDCCH. As another method, control information forphysical shared channel transmission of several component carriers maybe configured and transmitted as one PDCCH, and this is called a jointcoded PDCCH.

In order to perform downlink or uplink carrier aggregation, a connectionmay be set so that the PDCCH and/or PDSCH for performing transmission ofcontrol information and data may be performed according to the situationin a unique manner for a specific UE or each relay, or the base stationmay allocate component carriers which are the object of measurementand/or reporting as a process of preparing for performing a connectionsetting for transmission of the PDCCH and/or PDSCH. This is expressed ascomponent carrier allocation according to an arbitrary purpose.

At this time, in case the carrier allocation information is controlledin the L3 radio resource management (RRM), the base station may transmitthe information by a series of unique UE or relay RRC signaling(UE-specific or relay-specific RRC signaling) according to dynamicfeatures of the control, or may transmit the information through aseries of PDCCHs or a series of dedicated physical control channels fortransmission only of control information by L1/L2 control signaling.

FIG. 11 illustrates an example of a multi-carrier.

There are three DL CCs and three UL CCs, but the numbers of the DL CCsand UL CCs are not limited thereto. In each DL CC, the PDCCH and thePDSCH are independently transmitted, and in each UL CC, the PUCCH andthe PUSCH are independently transmitted.

Hereinafter, a multiple carrier system refers to a system which supportsa multiple carrier based on spectrum aggregation as described above.

In the multiple carrier system, contiguous spectrum and/ornon-contiguous spectrum aggregation may be used, or symmetricaggregation or non-symmetric aggregation may also be used.

In the multiple carrier system, a linkage between a DL CC and a UL CCmay be defined. The linkage may be constituted through EARFCNinformation included in the downlink system information, and isconstituted using the fixed DL/UL Tx/Rx separation relation. The linkagerefers to a mapping relation between a DL CC where the PDCCH carryingthe UL grant is transmitted and a UL CC using the UL grant.

Further, the linkage may be a mapping relation between a DL CC (or a ULCC) where data for HARQ is transmitted, and a UL CC (or a DL CC) wherethe HARQ ACK/NACK signal is transmitted. The base station may notify theUE of the linkage information as part of system information or the upperlevel message such as an RRC message. The linkage between the DL CC andthe UL CC may be fixed, but may also be changed between cells andbetween UEs.

A separate coded PDCCH means that the PDCCH is capable of carryingcontrol information such as resource allocation for the PDSCH/PUSCH onone carrier. That is, the PDCCH & the PDSCH and the PDCCH & PUSCHrespectively correspond to each other 1:1.

A joint coded PDCCH means that the PDCCH is capable of carrying resourceallocation for the PDSCH/PUSCH of a plurality of CCs. One PDCCH may betransmitted through one CC, or may be transmitted through a plurality ofCCs.

Hereinafter, an example of separate coding based on the PDSCH-PDSCH,which is a downlink channel, is illustrated, but this may also beapplied to the PDCCH-PUSCH relation.

In the multiple carrier system, two methods of cc scheduling arepossible.

A first method is transmitting a PDCCH-PDSCH pair in one CC. This CC iscalled a self-scheduling CC. Further, this means that the UL CC wherethe PUSCH is transmitted means that it becomes a CC linked to the DL CCwhere the PDCCH is transmitted.

That is, in the case of the PDCCH the PDSCH resource is allocated in thesame CC, or the PUSCH resource is allocated in the linked UL CC.

A second method is that a DL CC, where the PDSCH is transmitted, and aUL CC, where the PUSCH is transmitted, are determined regardless of theDL CC where the PDCCH is transmitted. That is, the PDCCH and the PDSCHare transmitted at different DL CCs, or the PUSCH is transmitted throughthe DL CC where the PDCCH is transmitted or the non-linked UL CC. Thisis called cross-carrier scheduling.

The CC where the PDCCH is transmitted is called PDCCH carrier,monitoring carrier or scheduling carrier, and the CC where thePDSCH/PUSCH is transmitted may be called the PDSCH/PUSCH carrier orscheduled carrier.

The cross-carrier scheduling may be activated or deactivated, the UE,where cross-carrier scheduling is activated, may receive a DCI includinga CIF. The UE may recognize which scheduled CC the PDCCH received fromthe CIF included in the DCI is control information about.

The DL-UL linkage predefined by the cross-carrier scheduling may beoverriding. That is, cross-carrier scheduling may schedule a CC otherthan the linked CC regardless of the UL-UL linkage.

FIG. 12 illustrates an example of the cross-carrier scheduling.

It is assumed that the DL CC #1 is linked with UL CC #1, DL CC #2 islinked with UL CC #2, and DL CC #3 is linked with UL CC #3.

A first PDCCH 1201 of DL CC #1 carries the DCI for the PDSCH 1202 of thesame DL CC #1. A second PDCCH 1211 of the DL CC #1 carries the DCI forthe PDSCH 1212 of the DL CC #2. A third PDCCH 1221 of the DL CC #1carries the DCI for the PUSCH 1222 of the non-linked UL CC #3.

The DCI of the PDCCH may include the carrier indicator field (CIF) forthe cross-carrier scheduling. The CIF indicates the DL CC or UL CCscheduled through DCI. For example, the second PDCCH 1211 may includethe CIF indicating the DL CC #2. The third PDCCH 1221 may include theCIF indicating the UL CC #3.

Further, the CIF of the third PDCCH 1221 may be notified not as a CIFvalue corresponding to the UL CC, but as the CIF value corresponding tothe DL CC.

That is, the CIF of the third PDCCH 1221 may indirectly indicate the ULCC #3 where the PUSCH has been scheduled by indicating the DL CC #3linked with the UL CC #3. This is because, if the DCI of the PDCCHincludes PUSCH scheduling and the CIF indicates the DL CC, the UE canrecognize the PUSCH scheduling on the UL CC linked with the DL CC. Assuch, it is possible to indicate a larger number of CCs than the methodof giving information on all DL/UL CCs using the CIF having a limitedbit length (e.g., a 3 bit CIF).

A UE, which uses cross-carrier scheduling, needs to monitor the PDCCH ofa plurality of scheduled CCs for the same DCI format within the controlregion of one scheduling CC. For example, if the transmission modes of aplurality of DL CCs are different, it is possible to monitor a pluralityof PDCCHs for different DCI formats for each DL CC.

Even if the same transmission mode is used, if the bandwidths of DL CCsare different, the size of the payload of the DCI format is differentunder the same DCI format, and thus a plurality of PDCCHs may bemonitored.

Consequently, when the cross-carrier scheduling is possible, the UEneeds to monitor the PDCCH for a plurality of DCIs in the control regionof the monitoring CC according to the transmission mode and/or bandwidthfor each CC. Hence, there is a need for constitution of a search spacesupporting the same, and monitoring of the PDCCH.

First, in a multiple carrier system, the following terms are defined.

UE DL CC set: A set of DL CCs scheduled so that the UE may receive thePDSCH.

UE UL CC set: A set of UL CCs scheduled so that the UE may receive thePUSCH.

PDCCH monitoring set: At least one set of DL CCs performing PDCCHmonitoring. The PDCCH monitoring set may be the same as the UE DL CCset, or a subset of the UE DL CC set. The PDCCH monitoring set mayinclude at least one of the DL CCs within the UE DL CC set. Further, thePDCCH monitoring set may be individually defined regardless of the UL DLCC set. The DL CC, which is included in the PDCCH monitoring set, may beset so that self-scheduling for the linked UL CC is always possible.

The UE DL CC set, the UE UL CC set and the PDCCH monitoring set may beset to be cell specific or UE specific.

Further, the following shows which DCI format the CIF may belong to.

-   -   If a CRC is scrambled as P-RNTI, RA-RNTI or TC-RNTI, the DCI        format does not include the CIF.

DCI formats 0, 1, 1A, 1B, 1D, 2, 2A and 2B, which can be received in theUE specific search space, may include the CIF if the CRC is scrambled(or masked) by the C-RNTI and SPS-RNTI.

FIG. 13 shows an example of a CC set. Here, we assumed that four DL CCs(DL CC #1, #2, #3, #4) as a UE DL CC set, two UL CCs (UL CC #1, #2) as aUE UL CC set, and two DL CCs (DL CC #2, #3) as a PDCCH monitoring set,have been allocated to the UE.

DL CC #2 within the PDCCH monitoring set transmits the PDCCH for thePDSCH of the DL CC #1/#2 within the UE DL CC set and the PDCCH for thePUSCH of the UL CC #1 within the UE UL CC set. The DL CC #3 within thePDCCH monitoring set transmits the PDCCH for the PDSCH of the DL CC#3/#4 within the UE DL CC set and the PDCCH for the PUSCH of the UL CC#2 within the UE UL CC set.

A linkage may be set between CCs included in the UE DL CC set, UE UL CCset and PDCCH monitoring set. In the example of FIG. 13, a PDCCH-PDSCHlinkage is set between the DL CC #2, which is a scheduling CC, and theDL CC #1, which is a scheduled CC. Further, the PDCCH-PUSCH linkage isset to the DL CC #2 and the UL CC #1. Further, a PDCCH-PDSCH linkage isset between the DL CC #3, which is a scheduling CC, and the DL CC #4,which is a scheduled CC. Further, a PDCCH-PUSCH linkage is set to the DLCC #3 and the UL CC #2. The base station may inform the UE ofinformation about such scheduling CC or the PDCCH-PDSCH/PUSCH linkageinformation through cell specific signaling or UE specific signaling.

Further, for each of the DL CCs within the PDCCH monitoring set, the DLCC and the UL CC may not be linked. After linking the DL CC within thePDCCH monitoring set with the DL CC within the UE DL CC set, the UL CCfor the PUSCH transmission may be limited to the UL CC linked to the DLCC within the UE DL CC set.

The CIF may be differently set according to the linkage of the UE DL CCset, UE UL CC set and PDCCH monitoring set.

Hereinafter, the ambiguity of the DCI detection in the cross-carrierscheduling and methods for solving the ambiguity problem will bedescribed.

First, the ambiguity of DCI detection in cross-carrier scheduling willbe described.

In the carrier aggregation system, in case the cross-carrier schedulingis not activated, the PDCCH monitoring CC set is always considered thesame as a UE specific DL CC set. In this case, separate signaling forthe PDCCH monitoring CC set does not need to be instructed. In contrast,in the case that cross carrier scheduling is activated, the PDCCHmonitoring CC set needs to be defined within the UE specific DL CC set.Hence, in this case, a separate signal for the PDCCH monitoring CC setmay be necessary.

FIGS. 14( a) and 14(b) illustrate a method for linking a DL CC includedin the PDCCH monitoring CC set with the CC transmitting the PDSCH/PUSCH.FIGS. 14( a) and 14(b) assume that all DL CCs form pairs with the ULCCs.

Option 1

Referring to FIG. 14( a), according to option 1, each CC transmittingPDSCH % PUSCH (hereinafter, referred to as PDSCH/PUSCH CC) is scheduledthrough one DL CC. That is, only one DL CC needs to be monitored for thePDSCH/PUSCH CC. In the DL CC having the CIF, the UE monitors the PDCCH,and the PDCCH of the DL CC may schedule at least one of the PDSCH forthe same DL CC and/or the PUSCH of the UL CC linked to the DL CC.

Option 2

Referring to FIG. 14( b), according to option 2, the PDSCH/PUSCH CC maybe scheduled through one or more DL CCs. The PDSCH/PUSCH CC may bescheduled through only one DL CC in each subframe, but may also bescheduled through different DL CCs in different subframes. In the DL CChaving the CIF where the UE monitors PDCCH, the PDCCH may schedule atleast one of the PDSCH of the same DL CC and/or the PUSCH of the linkedUL CC. Option 2 does not increase the number of blind decodings and/orthe CRC false detection rate compared to the system without the CIF.

If it is assumed that the UE attempts blind decoding 12 times in thecommon search space of each CC, in the case of the non cross-carrierscheduling, the maximum number of blind decoding attempts becomes 44.Further, in the case of cross carrier scheduling, the maximum number ofblind decoding-attempts may be calculated as follows.

$\begin{matrix}{\underset{i = 0}{\overset{M - 1}{Q}}44{{EN}(i)}} & {{Formula}\mspace{14mu} 3}\end{matrix}$

In the above formula 3, M indicates the number of DL CCs of the PDCCHmonitoring CC set. Each DL CC of the PDCCH monitoring CC set is numberedi=0, 1, . . . , (M−1), and N(i) represents the number of DL CCs whichcan be scheduled from the DL CC i.

For example, it is assumed that there are two DL CCs (hereinafter,referred to as the PDCCH monitoring DL CC) in the PDCCH monitoring CCset, and there are four CCs for transmitting the PDSCH/PUSCH (i.e.,PDSCH/PUSCH CC). In this case, it is assumed that the size of the commonsearch space of the PDCCH monitoring DL CC for the PDSCH/PUSCH CC is thesame as the comparing difference carrier scheduling.

In the case of option 1, the UE repeats blind-decoding one PDCCHmonitoring DL CC for two PDSCH/PUSCH CCs twice, and thus the maximumnumber of blind decoding attempts becomes 2×2×44=176. In contrast, inthe case of option 2, the UE should blind-decode the two PDCCHmonitoring DL CCs for four PDSCH/PUSCH CCs, and thus the maximum numberof blind decoding attempts becomes 4×2×44=352. That is, in option 2, amuch greater number of blind decoding attempts should be made.

When using option 1, in the case of the comparing difference carrierscheduling, the DL CC other than the PDCCH monitoring CC does not needto be monitored, Rel-8 blind decoding overhead is required for each DLCC. However, unlike option 2, there is a restriction in the scheduling,and thus it is difficult to support full flexible scheduling. When usingoption 2, the full flexible scheduling may be supported, but excessiveblind decoding complexity may be generated on the side of the UE.

A method for using advantages of options 1 and 2 will be describedbelow.

Option 3

The base station first sets the DL CC which transmits the PDCCH for thePDSCH/PUSCH CC. The DL CC having the CIF (where the UE monitors thePDCCH) may perform scheduling for at least one of the PDSCH of the sameDL CC and/or the PUSCH of the linked UL CC. At this time, in case thePDCCH has the same DCI payload size among the PDSCH/PUSCH CC, the searchspace may be shared.

FIGS. 15( a) and (b) illustrate the above described option 3 (amendedoption 1).

Referring to FIG. 15( a), the PDCCH monitoring DL CC #1 transmits thePDCCH for CC #1 and CC #2, and the PDCCH monitoring DL CC #2 transmitsthe PDCCH for CC #3 and CC #4. Here, in case the DCI payload size of thePDCCH for CC #2 is the same as the DCI payload size of the PDCCH for CC#3, the search space for CC #2 and CC #3 may be shared as in FIG. 15(b).

Hereinafter, the DL CC, where the UE monitors the PDCCH, is called themonitoring CC for convenience of explanation. Further, the DL CC, wherethe UE receives the PDSCH, is called the PDSCH CC, and the UL CC, wherethe UE transmits the PUSCH, is called the PUSCH CC. The PUSCH CC and thePUSCH CC are commonly called the scheduled CC.

For example, it is assumed that the scheduled CC #2 is linked to themonitoring CC #1, and the scheduled CC #3 is linked to the monitoring CC#2. In such case, the UE first monitors the monitoring CC #1 in order toreceive the PDCCH of the scheduled CC #2, and first monitors themonitoring CC #2 in order to receive the PDCCH of the scheduled CC #3.However, in the PDCCH of the scheduled CC #2 and the PDCCH of thescheduled CC #3, if the DCI sizes are the same, the search space may beset to be shared. That is, in case the DCI sizes are the same, the UEmay first monitor the PDCCH even in the DL CC other than the linkedmonitoring CC. For example, the UE may monitor the monitoring CC #2 aswell as the monitoring CC #1 for the scheduled CC #2.

The above option shares the search space for the PDCCHs only in the casein which the PDCCH for the scheduled CC, which can be received in one ormore monitoring CCs, has the same DCI payload size. Further, the (prior)link relation is maintained as in the above option 1 only in case thePDCCH for the scheduled CC, which can be received in one or moremonitoring CCs, has different DCI payload sizes. Through such a method,scheduling flexibility of the base station may be improved whilemaintaining a certain level.

At cross carrier scheduling, DCIs for one or more scheduled CCs may bedetected in the monitoring CC. For example, the DCIs for one or morescheduled CCs may be detected by the search space sharing in two or moremonitoring CCs as in the above option 3, or DCIs for one or morescheduled CCs may be detected by the search space sharing in onemonitoring CC. When sharing the search space between PDCCHs having thesame DCI size, a plurality of DCIs having the same DCI size may bedetected. In such case, the UE may recognize that the PDCCH belongs tothe UE itself through the CRC checking included in the process ofreceiving the PDCCH, but it may be difficult to determine the scheduledCC which the DCI having succeeded in detection is a DCI about. This iscalled ambiguity. (Sure is!)

For example, in the monitoring CC, which uses cross carrier scheduling,the DCI including the CIF and the DCI without the CIF in the searchspace may have the same DCI payload size. At this time, ambiguity occursbecause the UE cannot determine whether the detected PDCCH isinformation about the DCI including the CIF or information about the DCIwithout the CIF (in the case that cross carrier scheduling is used, ifthe CIFs are included in all DCIs in the monitoring CC, it is possibleto determine which scheduled CC the DCI is information about through theCIF, and thus ambiguity does not occur).

Further, if different CIF lengths coexist, even in if the DCIs includingCIFs of different lengths have the same payload size, the same problemmay occur.

That is, the above problem may occur in the following cases.

CASE 1. The downlink control information (DCI) transmitted to the commonsearch space (SS) without the CIF and the DCI transmitted to the UEspecific SS with the CIF are transmitted with the same size, and thesection of the transmitted common SS overlaps with the section of the UEspecific SS.

CASE 2. The DCI for the self-scheduling CC without the CIF and the DCIfor the cross-scheduling CC with the CIF have the same size and aretransmitted, and the section of the UE specific SS for theself-scheduling CC overlaps with the section of the UE specific SS forthe cross carrier scheduling (overlaps partially or entirely), or the UEspecific SS for the self-scheduling CC is shared with the UE specific SSfor cross-carrier scheduling.

That is, in case the DCI format including the CIF and the DCI formatwithout the CIF have the same DCI size, and the DCIs are transmitted tothe overlapping SS or shared SS, such a problem may occur.

FIG. 16 illustrates a case in which DCI ambiguity occurs.

It is assumed that the control information for CC #1 and CC #2, i.e.,the DCI, is transmitted through CC #1.

FIG. 16( a) illustrates an occurrence of ambiguity of the DCI when thecommon search space for CC #1 overlaps with the UE specific search spacefor CC #2.

As illustrated in FIG. 16( a), in a section where the common searchspace for CC #1 overlaps with the UE specific search space for CC #2, ifthe DCI transmitted to the CSS without the CIF and the DCI transmittedto the USS with the CIF are transmitted with the same size, DCIambiguity may occur.

FIG. 16( b) illustrates an example of occurrence of ambiguity of the DCIwhen the common search space for CC #1 completely overlaps with the UEspecific search space for CC #2.

As illustrated in FIG. 16( b), in a section where the common searchspace for CC #1 completely overlaps with the UE specific search spacefor CC #2, in case the DCI for the self-scheduling CC without the CIFand the DCI for the cross-scheduling CC with the CIF are transmittedwith the same size, the DCI ambiguity may occur.

FIG. 16( c) illustrates an example of occurrence of ambiguity of a DCIin case the common search space for CC #1 partially overlaps with the UEspecific search space for CC #2.

As illustrated in FIG. 16( c), in a section where the common searchspace for CC #1 partially overlaps with the UE specific search space forCC #2. in case the DCI for the self-scheduling CC without the CIF andthe DCI for the cross-scheduling CC with the CIF are transmitted withthe same size, DCI ambiguity may occur.

FIG. 16( d) illustrates an example of occurrence of ambiguity of a DCIin case the UE specific search space for CC #1 is shared with the UEspecific search space for CC #2.

As illustrated in FIG. 16( d), in a section where the common searchspace for CC #1 is shared with the UE specific search space for CC #2,in case the DCI for the self-scheduling CC without the CIF and the DCIfor the cross-scheduling CC with the CIF are transmitted with the samesize, the DCI ambiguity may occur.

That is, as shown in FIG. 16. the search space of the DCI for CC #1 maycompletely or partially overlap with the search space for the DCI for CC#2. The search space may be a common search space (CSS) or a UE specificsearch space (USS), or may be different for each CC. For example, thesearch space for CC #1 is the common search space, and the search spacefor CC #2 may be a UE-specific search space.

In case the search spaces overlap with each other, the DCI of Cc #1 orCC #2 may include the CIF or may not include the CIF. However, if thepayload size of the DCI of CC #1 is the same as that of the DCI of CC#2, it is unclear whether the DCI detected in the overlapping searchspace includes the CIF.

As another problem, in case the search spaces for different CCs overlapwith each other, the CIF values included in the DCI payload, which canbe blind-decoded in the overlapping search space, may be the same. Insuch a case, ambiguity may occur about how the DCI information sets,which are located after the CIF, should be understood. Particularly,such a problem may occur when one DCI is for uplink and the other DCI isfor downlink.

Hereinafter, in case PDCCH search spaces overlap in specific CCssuggested in the present invention, or the PDCCH search space is sharedbetween specific CCs and the DCIs having the same size are transmittedin the overlapping or shared section, various methods for resolvingambiguity for the DCI detection considered above will be specificallydescribed.

Method 1: Adding a Padding Bit

Method 1 is a method for resolving ambiguity of DCI detection in asection where the PDCCH search spaces overlap or are shared by addingthe padding bits to one DCI among the DCIs having the same size.

That is, method 1 resolves the DCI size ambiguity by applying anadditional padding bit to one of the DCIs where the DCI size ambiguityoccurs.

As an example, in CASE 1 where the DCI ambiguity occurs, the padding bitmay be set to be attached to the UE-specific DCI transmitted to the UEspecific SS of the same size.

Further, in CASE 2 where the DCI ambiguity occurs, the padding bit maybe set to be attached to the cross-carrier scheduling DCI or theself-scheduling DCI.

Method 2: Applying Additional Unique Identifier (RNTI)

Method 2 shows a method for resolving DCI detection ambiguity byperforming additional RNTI masking to one of DCIs having the same size.

As an example, in the case of CASE 1 where the DCI ambiguity occurs, theadditional RNTI may be set to be masked to the UE specific DCItransmitted in the UE specific SS of the same size.

Further, in the case of CASE 2 where the DCI ambiguity occurs, theadditional RNTI may be set to be masked to the cross-carrier schedulingDCI or to be masked to the self-scheduling DCI.

Method 3: Constituting SS so that the CSS does not Overlap with the USS.

Method 3 is a method for resolving ambiguity for the DCI detection bymaking the DCI having the same size not be transmitted in the specificsearch space by constituting the CSS and the USS in a manner that theydo not overlap with each other.

That is, Method 3 is a method for constituting the UE-specific SS, whichwill transmit the DCI of the UE specific SS having the same size as thatof the DCI transmitted in the common SS, in a manner that is alwaysdisjointed with the common SS.

As an example for constituting the CSS and the USS in a disjointedmanner, search space shifting may be used. In case the USS overlaps withthe common SS as a result of constituting by calculating the startpoint, etc. (e.g., using a hash function), the search section of the USSis set to be shifted by as much as a portion where the USS section doesnot overlap with the CSS. Such a method may be applied in CASE 1 whereDCI ambiguity occurs.

FIG. 17 shows that, in case the CSS overlaps with the USS, the shiftingis made by as much as the overlapping section so that the CSS does notoverlap with the USS according to an exemplary embodiment of the presentinvention.

Referring to FIG. 17, the CCE level of the CSS is 4, the CCE level ofthe USS is 4, and the CSS overlaps with the USS at CCE index 7. In thiscase, in order to prevent overlap between the CSS and the USS, the UEsets the start point of the USS to be shifted from CCE index 7 to CCEindex 8 by 1.

FIG. 17 illustrates only shifting of the USS, but the UE can performshifting of the CSS so that the CSS does not overlap with the USS.

Method 4: Constituting the specific search space for each CC in adisjointed manner.

Method 4 is a method of resolving ambiguity of DCI detection byconstituting the search space of a specific CC in a manner that does notoverlap with the search space of another CC.

The DCI size ambiguity problem is because PDCCHs having the same DCIsize (DCI without CIF and DCI with CIF) are transmitted in a shared oroverlapping search space. As a method for preventing such a problem, theCC specific SS of the specific CC is set to be always disjointed withthe CC specific SS.

Here, the SS shifting, etc. as in the above method 3 may also be used inmethod 4. Further, even if the DCI sizes become the same, the DCIambiguity may be resolved through modified method 1 or a method of notallowing the sharing of SS between different CCs such as SS sharing.

Method 4 may be applied to both CASES 1 and 2 where DCI ambiguityoccurs.

FIG. 18 illustrates a constitution of a search space so that the searchspaces for each CC do not overlap with each other according to anotherexemplary embodiment of the present invention.

Referring to FIG. 18, the search space for CC #1 is comprised of up toCCE indexes 2 to 5, the search space for CC #2 is comprised of up to CCEindexes 7-8, and the search space for CC #3 is comprised of up to CCEindexes 9 to 12 so that the search spaces for each CC do not overlap.

Method 5: DCI Detection Considering Priorities (1)

Method 5 is a method of resolving DCI ambiguity by detecting DCIs givingpriority to the UE specific DCI, the DCI for cross scheduling, and theDCI with the CIF transmitted to the UE specific search space in theoverlapping or shared search space.

According to Method 5, the base station is not allowed to transmit thecommon DCI to the common SS in the overlapping or shared section in casethe PDCCH search space overlaps or is shared. In this case, the UEdetermines that the DCI, which has been detected in the section wherethe CSS overlaps with the USS, is a DCI for the USS, and receives theshared channel, i.e., the PDSCH/PUSCH.

Further, method 5 is not to allow transmission of the DCI for theself-scheduling CC in the overlapping or shared PDCCH search spacesection. Hence, the UE determines that the DCI, which has been detectedin a section where the search space for the self-scheduling CC overlapsor is shared with the search space for the cross-scheduling CC, is a DCIfor the cross-scheduling CC, and thereafter receives the shared channel(PDSCH/PUSCH) and performs the feedback process.

That is, method 5 is to transmit DCIs with the CIF in the overlapping orshared PDCCH search space section. Hence, the UE gives priorities toDCIs with the CIF and decodes the DCI, which has been detected in theoverlapping or shared SS section, based on the DCI with the CIF, andthereafter receives the shared channel and performs the feedbackprocess.

Putting priority may mean performing blind decoding only for DCIs withthe CIF, or first performing blind decoding for the DCIs with the CIFand thereafter performing blind decoding for DCIs without the CIF.

Method 6: DCI Detection Considering Priorities (2)

Method 6 provides a method for resolving the DCI ambiguity by detectingthe DCI giving priority to the common DCI, the DCI for self-schedulingand DCI without the CIF transmitted to the common search space in thesection where the PDCCH search spaces overlap or are shared. That is,method 6 is a method for detecting the DCI by putting priority in amanner opposite to that of method 5.

That is, according to method 6, the base station is not allowed totransmit the UE specific SS DCI to the overlapping and shared PDCCHsearch space section. Hence, the UE determines that the DCI, which hasbeen detected in a section where the CSS overlaps with the USS, is a DCIfor the CSS, and receives the shared channel.

Further, according to method 6, the base station is not allowed totransmit the DCI for the cross-scheduling CC to the overlapping orshared PDCCH SS section. Hence, the UE determines that the DCI, whichhas been detected in a section where the SS for the self-scheduling CCoverlaps or is shared with the SS for cross-scheduling CC, is a DCI forthe self-scheduling CC, and thereafter receives the shared channel andperforms the feedback process.

That is, method 6 is to transmit DCIs without the CIF to the overlappingor shared PDCCH SS section. Hence, the UE gives priority to the DCIwithout the CIF, decodes the DCI, which has been detected in theoverlapping or shared SS section, based on the DCI without the CIF, andthereafter receives the shared channel and performs the feedbackprocess.

Here, giving priority may mean performing blind decoding only for DCIswithout the CIF, or first performing blind decoding for DCIs without theCIF and thereafter performing blind decoding only for the DCIs with theCIF as described in the above method 5.

FIG. 19 illustrates a method of resolving DCI ambiguity in case thePDCCH search space overlaps or is shared by giving priority to the DCIwithout the CIF according another exemplary embodiment of the presentinvention.

First, FIG. 19( a) illustrates a method of detecting a DCI correspondingto the CSS in an overlapping section when the CSS overlaps with the USS.

Referring to FIG. 19( a), in the case of a section where the searchspaces of the CSS and the USS overlap with each other, the UE determinesthat the DCI corresponding to the CSS is transmitted in the overlappingsection, and performs blind decoding for a plurality of candidatePDCCHs. As a result of the blind decoding, the UE receives commondownlink control information through the PDCCH corresponding to the CSSwhich has succeeded in decoding.

FIG. 19( b) illustrates a method of detecting a DCI for theself-scheduling CC in an overlapping section in case the search spacesbetween the USSs completely overlap with each other.

Referring to FIG. 19( b), in case the search space of the USS for CC #1completely overlaps with the search space of the USS for CC #2, the UEdetermines that the DCI corresponding to self-scheduling is transmittedin the overlapping section, and performs blind decoding for a pluralityof candidate PDCCHs. As a result of the blind decoding, the UE receivesdownlink control information through the PDCCH corresponding to theself-scheduling which has succeeded in decoding.

FIG. 19( c) illustrates a method of detecting the DCI for theself-scheduling CC in an overlapping section in case the search spacesbetween the USSs partially overlap with each other.

Referring to FIG. 19( c), in the case of a section where the searchspaces of the USS for CC #1 and the USS for CC #2 partially overlap witheach other, the UE determines that the DCI corresponding toself-scheduling is transmitted in the overlapping section, and performsblind decoding for a plurality of PDCCHs. As a result of the blinddecoding, the UE receives downlink control information through the PDCCHcorresponding to the self-scheduling which has succeeded in thedecoding.

FIG. 19( d) illustrates a method of detecting a DCI for theself-scheduling CC in a shared section in the case of sharing the USSsof different CCs.

Referring to FIG. 19( d), in case the search space of the USS for CC #1is shared with the search space of the USS for CC #2, the UE determinesthat the DCI corresponding to the self-scheduling is transmitted in theshared section, and performs blind decoding for a plurality of candidatePDCCHs. As a result of the blind decoding, the UE receives downlinkcontrol information through the PDCCH corresponding to theself-scheduling which has succeeded in decoding.

Method 7: Detecting a DCI by Giving Priority to the Primary CC.

Method 7 is a method for resolving the DCI ambiguity by limiting theDCI, which is transmitted in the overlapping or shared PDCCH searchspace section, to the DCI for the primary CC.

Here, the primary CC may be defined for each of UEs, and in case one ormore PDCCH monitoring CCs are allocated to the UE, the primary DL/UL CCmay be defined for each PDCCH monitoring CC. The expression “primary CC”may be changed to another expression, but regardless of the expression,the DCI size ambiguity may be resolved by setting one of PDSCH/PUSCHCCs, which can perform scheduling in the PDCCH monitoring CC, to aprimary CC, and using the same in the DCI priority setting.

The primary CC for each PDCCH monitoring CC may be set as the UL CClinked on the system setting with the PDCCH monitoring DL CC (becausethe PDSCH is transmitted as DL CC), the CC having the primary linkagewith the PDCCH monitoring CC, or the DL/UL CC which is the object of theself-scheduling in the PDCCH monitoring CC, etc.

That is, according to method 7, the UE determines that the DCI, whichhas been detected in the overlapping or shared SS section, is a DCI forthe primary CC, and thereafter receives a shared channel and performsthe feedback process.

Method 8: Not Detecting DCI in a Section where the Search Spaces Overlapor are Shared.

Method 8 provides a method of not searching for a corresponding DCI incase ambiguity occurs due to equality of sizes of different DCIs as SSsoverlap with each other when the UE decodes SSs.

For example, if the case of the DCI without CIF and the DCI with the CIFfor other CCs have the same size, when performing a DCI search, the UEincludes only the DCI without the CIF for other CCs in search candidate,and does not include the DCI with CIF for other CCs in the searchcandidates. As such, it is possible to prevent occurrence of ambiguityincluding the UE of the same length.

Here, whether the DCI with the CIF may be omitted from the search or theDCIs without the CIF would be included may be configured throughsignaling, or may be predefined (e.g., predefined selection).

According to the above methods 1 to 8, the DCI ambiguity occurs in anoverlapping or shared search space as the CIF is not included in theDCI.

Hence, if the CIFs are all included in the DCIs of the fallback mode,the ambiguity problem does not occur in the UE SS. The same size DCI maybe included in the common SS, but the RNTI value may be differently setfor the DCI, and thus distinction is possible. However, in the case of aform that maintains Rel-8 mode, the DCIs of the same length may overlapwith each other in the state in which the CIF is not attached.

For example, the DCIs corresponding to the fallback for different CCsmay not include the CIF. In this case, both do not include the CIF, andthere is no way to distinguish them. Hence, when defining the DCIwithout the CIF, it is desirable to define only the SS area where theSSs do not overlap with each other.

For example, when there is a DCI without CIF among DCIs for a specificCC, if the DCI without CIF for another CC overlaps with the SS (and thelengths of the DCIs are the same), the DCI without the CIF for the CC isdecoded by giving priority to the SS for a specific CC, the DCI withoutthe CIF for another CC is not defined in the overlapping search section.Further, the above described methods may be applied to the DCI withoutthe CIF which is a problem.

If the SS, which uses the UE, is commonly defined for all CCs, thereshould be no ambiguity for sizes of the DCIs which should be searchedfor by the UE. To this end, the above defined methods may be applied.Further, if the sizes are the same only for the DCI without the CIF, theshared SSs may be defined in a disjointed manner and then use thedefined SSs.

Here, in case the distinctive UE specific SS overlaps with the common SSwhere common channel information is transmitted, the area may be definedas where scheduling only DCIs for the same carrier. The CCs may bearbitrarily defined for other SSs.

Method 9: Bit Level Scrambling, Bit Level Reverse.

Method 9 is a method for resolving the DCI size ambiguity problemthrough bit level scrambling.

Method 9 may use bit level scrambling so that the USS may bedistinguished from the CSS. For example, the scrambling code A for theUSS and the scrambling code B for the CSS may be used.

Further, in a section where the SS of the self-scheduling PDCCH overlapsor is shared with the SS of the cross-scheduling PDCCH, the bit-levelscrambling may be used so that the self-scheduling PDCCH without CIF canbe distinguished from the cross-scheduling PDCCH with the CIF.

The scrambling code for the DCI with the CIF may be distinguished fromthe scrambling code for the DCI without the CIF, and may then be used.

The bit level scrambling may be applied in various steps such as 1)information bits (before CRC attachment), 2) information bits+CRC (afterCRC attachment), and 3) after channel encoding.

Method 10: Removing SS for an Arbitrary DCI in a Section where DCI SizeAmbiguity Occurs.

Method 10 illustrates a method for resolving the problem by removing theSS for the DCI with the CIF or the SS for the DCI without the CIF in theDCI ambiguity section in FIGS. 16( a) to 16(d).

That is, the USS (or CSS) may be removed in a section where the CSSoverlaps with the USS. Further, in a section where the SS for theself-scheduling DCI overlaps or is shared with the SS for thecross-scheduling DCI, the SS for the self-scheduling DCI or the SS forthe cross-scheduling DCI may be set to be removed.

There should be a mutual promise between the UE and the base station todetermine which DCI's SS is to be removed in the ambiguity section.Further, it is possible to be informed through signaling at the time ofcross carrier scheduling activation.

In case the DCI with the CIF and the DCI without the CIF come to havethe same payload size, the PDCCH DCI, which has been detected accordingto a promised or known rule, may be analyzed based on the DCI with theCIF or the DCI without the CIF.

Method 10 causes the same result as that of the above priority solution(methods 5 and 6), but the configuration is different.

However, in method 10, the blocking probability of the PDCCH mayincrease in terms of the DCI transmitted to the removed SS.

Method 11: Removing an SS for an arbitrary DCI in a section where theDCI size ambiguity occurs and sequentially adding SSs by as many asremoved.

Method 11 is a method for maintaining blocking probability which is aproblem in method 10.

In the ambiguity section, the method of maintaining the SSs for one ofDCIs with the same size and removing the SSs for the other DCIs is thesame as that of method 10. In order to make the blocking probabilitysame as that of the case where the SSs are not removed, the method ofsequentially adding the removed SSs is suggested.

That is, when the CSS overlaps with the USS, the USSs of the overlappedportion may be removed, and new USSs may be sequentially added by asmany as removed (indexing may be done in a circular manner), or the CSSsmay be removed, and new CSSs may be sequentially added by as many asremoved.

In a section where the SS for the self-scheduling DCI overlaps or isshared with the SS for the cross-scheduling DCI, the SSs for theself-scheduling DCI may be removed and new SSs for the self-schedulingDCI may be sequentially added by as many as removed, or the SSs for thecross-scheduling DCI may be removed and new SSs may be sequentiallyadded by as many as removed.

At this time, the added SSs may be constituted in the CCE row outsidethe ambiguity section.

Method 12: Allocating an Exclusive SS, and Reflecting this Allocation inan SS Setting Parameter so that an Ambiguity Section is not Generated.

Method 12 is similar to methods 3 and 4. The CSS and the USS may beexclusively set, the SS of the self-scheduling DCI and the SS of thecross-scheduling DCI may be exclusively set, or the SS of the DCI withthe CIF and the SS of the DCI without the CIF may be exclusively set.

In case the CSS and the USS are exclusively set, a value, which canalways set the SS to be disjointed with the CSS, may be included in theUSS setting parameter. Since the CSS is a SS, which always exists in afixed location section, and thus a method of moving the USS iseffective.

In case the SS of the self-scheduling DCI and the SS of thecross-scheduling DCI are exclusively set, a value, which can set thecross-scheduling DCI SS to be always disjointed with the self-schedulingDCI SS, may be included in the cross-scheduling SS setting parameter.The same is applied to the SS of the DCI with the CIF and the SS of theDCI without the CIF.

For example, the value may be a parameter indicating shifting orhopping, etc.

Here, a parameter for exclusively setting the SS is not always a fixedvalue, but may be set to a different value every time according to theconfiguration of the SS.

Method 13: Method of resolving the ambiguity problem through x-bit(e.g., x=1) indication in the DCI.

In order to resolve the DCI size ambiguity problem, a bit, which givesinformation about the DCI, may be added to the DCI.

For example, 1 bit indication about whether the DCI is a DCI to betransmitted to the USS or to the CSS may be given to the DCI. Further,whether the DCI is a self-scheduling DCI or a cross-scheduling DCI andwhether the DCI is a DCI with the CIF or a DCI without the CIF may benotified through the x-bit indication in the DCI format, and thus the UEmay perform PDCCH decoding without size ambiguity.

Here, since may recognize whether the DCI is a DCI with the CIF only ifthe UE can determine the bit at a fixed position, and thus the x-bitindication should be set to be transmitted to a position always fixed onthe DCI payload.

A fixed position means an always fixed position regardless of the DCIsize.

For example, the forefront x-bit and the very last x-bit may be used.

Method 14: A Method of Solving a Problem Through Puncturing in a DCITransmitted to a Section where the DCI Size Ambiguity Occurs.

Method 14 is a method of solving a problem by differentiating DCI sizesby bit puncturing among one or more DCIs transmitted to the ambiguitysection.

In case the SSs of the USS and the CSS overlap with each other, in a DCItransmitted in a USS transmitted to an overlapping SS section (or a DCItransmitted in the CSS, but it appears to be more reasonable to puncturethe DCI transmitted in the U), at least one bit is punctured. Forexample, in the case of one bit puncturing, after CRC-encoding aninformation bit, one of 16 bits of the CRC is punctured. That is, if theinformation bit is 24 bits, it should originally be 40 bits, but itbecomes 39 bits due to the CRC puncturing. Channel encoding is performedwith this.

In a cross-scheduling DCI (or self-scheduling DCI) transmitted in asection where the SS of the self-scheduling DCI overlaps or is sharedwith the SS of the cross-scheduling DCI, at least one bit is punctured.

When transmitted in an SS where the DCI with the CIF and the DCI withoutthe CIF overlap or are shared, at least one bit may be set to bepunctured in a DCI with the CIF (or the DCI without the CIF). In thiscase, the probability of false detection is increased by ½.

FIG. 20 is a block diagram illustrating a radio communication systemaccording to an exemplary embodiment of the present invention.

A base station 2010 includes a controller 2011, a memory 2012, and aradio frequency (RF) unit 2013.

The controller 2011 implements suggested functions, processes and/ormethods. Layers of the radio interface protocol may be implemented bythe controller 2011.

The controller 2011 may control to operate carrier aggregation and totransmit the PDCCH corresponding to the CSS or the PDCCH without the CIFin a section where the PDCCH search space overlaps or is shared.

The memory 2012 is linked to the controller 2011, and stores a protocolor a parameter for carrier junction. The RF unit 2013 is linked to thecontroller 2011, and transmits and/or receives radio signals.

A UE 2020 includes a controller, a memory 2022, and a radio frequency(RF) unit 2023.

The controller 2012 implements suggested functions, processes and/ormethods. The layers of the radio interface protocol may be implementedby the controller 2021. The controller 2021 may control to operate thecarrier junction and to receive the PDCCH corresponding to the CSS orthe PDCCH without the CIF in a section where the PDCCH search spacesoverlap or are shared.

The memory 2012 is linked with the controller 2021. and stores aprotocol or a parameter for carrier junction operation. The RF unit 2013is linked with the controller 2021, and transmits and/or receives radiosignals.

The controllers 2011 and 2021 may include an application-specificintegrated circuit (ASIC), another chipset, logic circuit and/or dataprocessing apparatus. The memories 2012 and 2022 may include a read-onlymemory (ROM), a random access memory (RAM), a flash memory, a memorycard, a storage medium and/or other storage devices. The RF units 2013and 2023 may include a baseband circuit for processing radio signals.When an exemplary embodiment is implemented by software, the abovedescribed scheme may be implemented as a module (process, function,etc.) which performs the above described function. The module may bestored in memories 2012 and 2022 and may be executed by the controllers2011 and 2021. The memories 2012 and 2022 may be positioned inside oroutside the controller 2011 and 2021, and may be connected with thecontrollers 2011 and 2021 in various well-known manners.

What is claimed is:
 1. A method for receiving a downlink controlinformation (DCI) from a base station (BS) by a user equipment (UE) in awireless communication system, the method comprising: monitoring aplurality of physical downlink control channel (PDCCH) candidates havingthe same payload size in a common search space and a UE-specific searchspace on a primary cell to receive the DCI, wherein the common searchspace and the UE-specific search space are overlapped; and if the UE isconfigured with a carrier indicator field (CIF), determining that only aPDCCH in the common search space is transmitted from among the pluralityof PDCCH candidates.
 2. The method according to claim 1, wherein the DCIcarried by a PDCCH candidate in the UE-specific search space includes aCIF, and the DCI carried by a PDCCH candidate in the common search spacedoes not include a CIF.
 3. The method according to claim 1, wherein anaggregation level of a PDCCH candidate in the common search space is thesame as that of a PDCCH candidate in the UE-specific search space. 4.The method according to claim 1, wherein the DCI carried by a PDCCHcandidate in the common search space has at least one different DCIfield from that of the DCI carried by a PDCCH candidate in theUE-specific search space.
 5. The method according to claim 1, whereinthe monitoring the plurality of PDCCH candidates includes performing ablind decoding for the plurality of PDCCH candidates, and the blinddecoding includes performing cyclic redundancy check (CRC) de-scramblingfor each of PDCCH candidates using a radio network temporary identifier(RNTI).
 6. A user equipment (UE) configured to receive a downlinkcontrol information (DCI) from a base station (BS) in a wirelesscommunication system, the UE comprising: a radio frequency (RF) unit fortransmitting and receiving a radio signal; and a controller associatedwith the RF unit, wherein the controller is configured to monitor aplurality of physical downlink control channel (PDCCH) candidates havingthe same payload size in a common search space and a UE-specific searchspace on a primary cell to receive the DCI wherein the common searchspace and the UE-specific search space are overlapped, and wherein ifthe UE is configured with a carrier indicator field (CIF), thecontroller is configured to determine that only a PDCCH in the commonsearch space is transmitted from among the plurality of PDCCHcandidates.
 7. The UE according to claim 6, wherein the DCI carried by aPDCCH candidate in the UE-specific search space includes a CIF, and theDCI carried by a PDCCH candidate in the common search space does notinclude a CIF.
 8. The UE according to claim 6, wherein an aggregationlevel of a PDCCH candidate in the common search space is the same asthat of a PDCCH candidate in the UE-specific search space.
 9. The UEaccording to claim 6, wherein the DCI carried by a PDCCH candidate inthe common search space has a different DCI field from that of the DCIcarried by a PDCCH candidate in the UE-specific search space.
 10. The UEaccording to claim 6, wherein the controller is configured to perform ablind decoding for the plurality of PDCCH candidates, and the blinddecoding includes performing cyclic redundancy check (CRC) de-scramblingfor each of PDCCH candidates using a radio network temporary identifier(RNTI).